The present invention is directed to a regenerative pump, sometimes referred to as a toric pump, especially designed for economical mass production which is capable of developing higher pressures and flow rates at higher efficiencies than other pumps of comparable design and operating speed, by modifications made to the impeller and/or housing.
In an automotive emission control system, a pump supplies air as required to the exhaust system between the manifold and the catalytic converter. In conventional regenerative pumps intended for use in an automotive emission control system, the impeller has straight radially extending blades at its outer periphery and is driven in rotation between a pump housing and a cover formed with a pump chamber. The pump chamber is formed symmetrical with respect to the rotatable impeller, and the surfaces of the housing and the cover. Further descriptions of toric pumps of this construction can be obtained from U.S. Pat. Nos. 5,302,081; 5,205,707 and 5,163,810.
Over time, industry needs have changed as restrictions on emissions have changed. It is now desirable to provide more air to an automotive emission control system than was previously required. Currently, it is desirable to provide at least between 19 and 20 cubic feet per minute (cfm). It is also desirable to meet the minimum fluid flow requirements while maintaining the same size housing. To meet these new fluid flow requirements, it has been necessary to double, and in some instances quadruple, the currently existing fluid flow rates of regenerative single stage pumps. Up to this point in time, the typical regenerative pump used in automotive emission control system applications has been capable of achieving a fluid flow rate of only 4 cubic feet per minute (cfm) at approximately 40 inches (H2O) head, and therefore, it is desirable in the present invention to provide a greater fluid flow output at the same or greater pressure for a given size housing configuration. It is further desirable in the present invention to reduce the electrical current or power requirements for a motor used in an electric motor driven pump for a given pressure and/or flow output. It is also desirable in the present invention to reduce the rotational speed of the motor required for a given pressure and/or flow rate output. Additionally, it is desirable in the present invention to increase overall efficiency and to provide for longer life and enhance reliability of regenerative pumps, and in particular, single stage, double channel, electrical air pumps or compressors.
In a regenerative pump according to the present invention, the rotor vanes of the peripheral regenerative pump are arcuate when viewed from the side, with the upper and lower portions curved forward in the direction of rotation. Preferably, a chamfer, or similar relief is formed on the convex side of the inner portion of all vanes. Bending the root portion of the vane to face forward and the addition of the chamfer are aimed at reducing pressure energy losses in the fluid entry region. Energy losses in the fluid entry region are the dominant loss in this type of regenerative pump. Prototypes of an impeller according to the present invention have been produced and tested. The test results have indicated a pressure increase, for the same rotational speed, of no less than 60% over the whole operating range and no less than 100% over a substantial portion of the whole operating range. In the tests, flow also increases over the operating range. Such dramatic increases in pressure and flow were unexpected.
The present invention also concerns double channel regenerative pumps of the type embodying a central rotor with vanes extending generally radially, either in a straight radial fashion, or in an arcuate fashion. Previously, it has been difficult to achieve a proper matching of the output of such a regenerative pump or compressor to the requirements of a particular application. Although some matching could be achieved by judicial choice of shaft rotational speed, pump efficiency can suffer in the process. Typically, a pump of this type includes a housing means for mounting a drive motor and one of the side channels, a rotor with generally radially extending vanes at its outer region on one or more axial sides of the rotor, and a cover sealingly engaged with the housing and a second side channel. The present invention allows matching of a pump""s capacity to the requirements of a particular application without changing shaft rotational speed. Previously the channels and the housing and cover have been equal, or symmetrical in cross-section, and differ only at the channel ends where it is common to place transfer inlet and delivery passages from the housing channel to ducts in the cover or housing. In the present invention, the channels of the housing and cover are formed in a manner which is not symmetrical. The cover, which is freely accessible, can be replaced by alternative covers having channels of various depths, or the cover can be spaced axially outwardly from the impeller by insertable spacers of various depths to change the effective depth of the channel in the cover. Thereby, the specific output of the pump may be varied to suit different fluid flow requirements by providing the appropriate asymmetrical depth of channel. Prototypes of asymmetrical side channels have been constructed and tested. These tests show that a change in capacity of at least 20% can be achieved by varying the axial depth of the channel without loss in the overall efficiency of the regenerative pump. The prototype of the present invention that was tested included a spacer plate inserted between the housing and the cover. The plate increased one of the side channels by a depth according to the thickness of the plate. Thus, a deeper channel can be provided without requiring the costly and time consuming measure of manufacturing a new cover. The magnitude of enhancement to pump performance was unexpected.
A regenerative pump for adding energy to a fluid, according to the present invention, includes an impeller having an axis of rotation and axially spaced, radially extending first and second surfaces. A radially split casing encloses the impeller and has a fluid inlet and a fluid outlet separated by a stripper. The stripper generally has a close clearance to a periphery of the impeller. The casing has axially spaced, radially extending first and second side walls facing the first and second surfaces respectively. Axially and radially extending blade means is formed on an outer radial periphery of the pump for driving fluid from the inlet toward the outlet as the impeller rotates about the axis of rotation. Means, formed in at least one side wall of the casing, directs fluid back toward the impeller.
The blade means preferably includes a plurality of vanes spaced circumferentially around the outer radial periphery of the impeller. Each vane has a radially inward base portion extending in a generally trailing direction with respect to rotation of the impeller and a radially outward tip portion extending in a generally leading direction with respect to rotation of the impeller.
Chamfer means is preferably formed on the base portion of each vane for deflecting fluid from the inlet toward the pocket defined between two adjacent vanes and the casing. Preferably, the chamfer means is formed on a trailing edge of the base portion of each vane. The chamfer means may be formed at an angle with respect to a radially extending plane normal to the axis of rotation of the impeller at a range selected from between 10xc2x0 and 45xc2x0 inclusive. Alternatively, the chamfer means may be formed as a curved surface having a predetermined radius connecting a generally radially extending surface of each vane to a generally axially extending surface of the respective vane along a trailing edge.
The blade means may include a plurality of vanes spaced circumferentially around the outer radial periphery of the impeller, where each vane is bent in radial direction with respect to the axis of rotation of the impeller about an axis generally parallel with the axis of rotation of the impeller. Alternatively, the blade means may include at least one set of radially bent vanes with respect to the axis of rotation, where the set of vanes is defined by at least two circumferentially spaced vanes collaborating with one another to form a single circular annulus.
The base portion of each vane preferably forms an entry angle with respect to a radially extending plane normal to the axis of rotation of the impeller in a range selected from between 20xc2x0 and 30xc2x0 inclusive. The tip portion preferably forms an exit angle with respect to a radially extending plane normal to the axis of rotation of the impeller in a range selected from between 20xc2x0 and 45xc2x0 inclusive.
The impeller has a generally radially extending plane or web normal to the axis of rotation and connected to the blade means. The web extends radially into the blade means to a position generally midway between the base and the tip of each vane. Preferably, the right angle surfaces, formed by the web and an annular hub of the impeller supporting the base of each vane, is filled in to provide an angled, stepped, or preferably radially curved transition between the axially extending hub portion of the impeller and the radially extending web between each adjacent set of vanes.
The fluid directing means preferably includes a fixed shaped surface. The fluid directing means may include at least one of the first and second side walls having a generally ring-shaped, side channel portion formed in the casing around the axis of rotation for directing fluid helically back into contact with the blade means as the impeller rotates. Preferably, the side channel portion is generally perpendicular to and along an arc of constant radius centered on the axis of rotation. In the preferred embodiment, the fluid directing means includes each of the first and second side walls having a generally ring-shaped side channel portion formed therein around the axis of rotation of the impeller for directing fluid helically back into contact with the blade means as the impeller rotates. Preferably, the fluid directing side channel portion of one of the first and second side walls is enlarged with respect to the other fluid directing side channel portion. Preferably, the enlarged one of the side channel portions is enlarged in the axial direction. The fluid directing means preferably is formed asymmetrically in the first and second side walls of the casing around the axis of rotation of the impeller.
In an additional embodiment, a means for defining a flow path between the fluid inlet and the fluid outlet is formed in at least one of the first and second side walls of the casing. The flow path defining means is tapered so that the cross-sectional area at the fluid inlet is greater than the cross-sectional area at the fluid outlet. The flow path defining means may include the side channel portions wherein the side channel portions preferably taper axially inward toward said impeller at a constant slope from said fluid inlet to said fluid outlet.
Regenerative pumps have traditionally been constructed, when there are two channels, with side channels equal in cross-section. The present invention demonstrates that unequal channels cause no significant loss in efficiency or other deleterious effects. The option of using unequal channels facilitates convenient capacity modifications so that a single pump design may have its pumping characteristics modified to satisfactorily meet more than one specific application requirement. The asymmetric channels according to the present invention may be used with a standard configuration impeller for a regenerative pump, or may be used in combination with the arcuate vane impeller configuration according to the present invention for further performance enhancement. The rear swept lower, or entry, or base portion of the vane with forward swept tip approximately midway up from the root of the vane, as previously described with respect to the present invention, can advantageously be used in combination with the asymmetric channels. The arcuate vane configuration, as previously described, can also include the modification of chamfer means for easing entry of fluid, particularly where the entry angle is large relative to the impeller axis. As the flow rate is reduced and the pressure rises, the ease of entry for fluid into the impeller is a feature that is associated with results that reveal improved maximum pressure for a given shaft speed and higher efficiency. As previously described, the chamfer means may also take an alternative curvilinear profile.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.